94 trailer light problems

When i hook a trailor to my truck and hook it to the light hook up and turn on the tail lights and hit the breaks it blows that juction area where the trailor light hook up connects both blinkers. When this blows it kills my blinkers and reverse lights. I can replace that connecter all my lights start working till i hook a trailor up to it and it does not matter which one i have tried 5 different trailors some flat beds some box beds.